There exist wireless communication techniques for transmitting and receiving information using wireless communication. For example, communication methods have been proposed for transmitting and receiving information between information processing devices using a wireless local area network (LAN).
If the information processing device is a mobile object, for example, a battery is often used as its power source. That means it is important to reduce power consumption in order to prolong the operating time of the information processing device. Thus the Institute of Electrical and Electronic Engineers (IEEE), which is a wireless LAN standardization organization, has proposed in its IEEE 802.11 standards techniques for allowing the information processing device, when not required to communicate, to transition from a normally active awake state to a doze state in which signals are not transmitted or received. The techniques are intended to reduce power consumption.
With the proposed techniques, an extension unit in the doze state enters the awake state at regular intervals to determine, using a signal from its base station, whether or not the base station is buffering any data destined for the own device. The signal is a traffic indication map (TIM) in a beacon frame. If it is determined that data destined for the own device is buffered, the extension unit transmits a data request frame named a Power Save Poll (PS-Poll) to the base station to receive the data therefrom. After receiving the data, the extension unit returns to the doze state. The PS-Poll frame constitutes information that communicates both the awake state of the extension unit and its data transmission request.
If there are multiple extension units, they may transmit multiple PS-Poll frames. With multiple PS-Poll frames transmitted concurrently, a collision avoidance algorithm may be activated, which may lead to a time loss.
As another example, upon receipt of a PS-Poll frame from an extension unit, the base station transmits data to that extension unit in response to the frame. In this case, no other extension unit is allowed to carry out its transmission while the data transmission is underway. As a result, it can take more time for the other extension units to return to the doze state, which may increase their power consumption.
There have been proposed techniques for reducing the time loss resulting from the avoidance of PS-Poll collision and from the ongoing communication by some other extension unit. For example, there has been proposed a data transmission and reception system that sets the time at which each extension unit is allowed to transmit a PS-Poll frame, the system notifying the extension units of such time settings beforehand to avoid PS-Poll collision (e.g., see PTL 1).